1 files changed, 156 insertions, 0 deletions
diff --git a/src/condition.rs b/src/condition.rs
new file mode 100644
index 0000000..7a873a8
--- /dev/null
+++ b/src/condition.rs
@@ -0,0 +1,156 @@
+use std::cmp::{max, min};
+
+use chrono::{Datelike, NaiveDate, NaiveDateTime, NaiveTime};
+use serde::{Deserialize, Serialize};
+use Direction::*;
+use Edge::*;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub enum Condition {
+    From(Box<Condition>),
+
+    Or(Vec<Condition>),
+    And(Vec<Condition>),
+    Invert(Box<Condition>),
+
+    Equal {
+        prop: Property,
+        value: i32,
+        modulus: Option<i32>,
+    },
+    Range {
+        prop: Property,
+        min: i32,
+        max: i32,
+        modulus: Option<i32>,
+    },
+}
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub enum Property {
+    Year,
+    Monthofyear,
+    Weekofmonth,
+    Dayofyear,
+    Dayofmonth,
+    Dayofweek,
+    Hour,
+    Minute,
+    Second,
+    Unix,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Range<T>(T, T);
+impl<T: PartialOrd + PartialEq> Range<T> {
+    pub fn includes(&self, a: T) -> bool {
+        a > self.0 && a < self.1
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum Edge {
+    Start,
+    End,
+}
+#[derive(Debug, Clone, Copy)]
+pub enum Direction {
+    Forward,
+    Backward,
+}
+
+impl Condition {
+    pub fn find(&self, edge: Edge, dir: Direction, from: NaiveDateTime) -> Option<NaiveDateTime> {
+        match self {
+            Condition::And(_) => todo!(),
+            Condition::Or(cs) => {
+                cs.iter()
+                    .filter_map(|c| c.find(edge, dir, from))
+                    .reduce(match dir {
+                        Forward => min,
+                        Backward => max,
+                    })
+            }
+            Condition::From(c) => todo!(),
+            Condition::Invert(c) => c.find(edge.invert(), dir, from),
+            Condition::Equal {
+                prop,
+                value,
+                modulus,
+            } => {
+                let geq = match dir {
+                    Forward => |a: i32, b: i32| a >= b,
+                    Backward => |a: i32, b: i32| a < b,
+                };
+                let off = match edge {
+                    Start => 0,
+                    End => 1,
+                };
+                match prop {
+                    Property::Year => {
+                        if geq(from.year(), *value + off) {
+                            None
+                        } else {
+                            Some(NaiveDateTime::new(
+                                NaiveDate::from_ymd(*value + off, 1, 1),
+                                NaiveTime::from_hms(0, 0, 0),
+                            ))
+                        }
+                    }
+                    Property::Monthofyear => todo!(),
+                    Property::Weekofmonth => todo!(),
+                    Property::Dayofyear => todo!(),
+                    Property::Dayofmonth => todo!(),
+                    Property::Dayofweek => todo!(),
+                    Property::Hour => todo!(),
+                    Property::Minute => todo!(),
+                    Property::Second => todo!(),
+                    Property::Unix => todo!(),
+                }
+            }
+            Condition::Range {
+                prop,
+                min,
+                max,
+                modulus,
+            } => todo!(),
+        }
+    }
+}
+
+impl Edge {
+    pub fn invert(self) -> Self {
+        match self {
+            Edge::Start => Edge::End,
+            Edge::End => Edge::Start,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::{Condition, Direction, Edge, Property};
+    use chrono::NaiveDateTime;
+    use std::str::FromStr;
+
+    #[test]
+    fn a() {
+        let cond = Condition::Equal {
+            modulus: None,
+            prop: Property::Year,
+            value: 2023,
+        };
+
+        let dt = NaiveDateTime::from_str("2022-06-07T13:37:48").unwrap();
+        assert_eq!(
+            cond.find(Edge::Start, Direction::Forward, dt).unwrap(),
+            NaiveDateTime::from_str("2023-01-01T00:00:00").unwrap(),
+        );
+        assert_eq!(
+            cond.find(Edge::End, Direction::Forward, dt).unwrap(),
+            NaiveDateTime::from_str("2024-01-01T00:00:00").unwrap(),
+        );
+        assert_eq!(cond.find(Edge::End, Direction::Backward, dt), None);
+        assert_eq!(cond.find(Edge::Start, Direction::Backward, dt), None);
+    }
+}